Preparation of 7-dehydro sterols



Patented May 22, 1945 PREPARATION OF 7-DEHYDRO STEROLS Hans R.Rosenberg, Wilmington, Del.', assignor to E..I. du Pont de Nemours &Company, Wilmington, Del., a corporation of Delaware No Drawing.Application January 14, 1942,

Serial No. 426,785

4 Claims.

This invention pertains to the preparation of organic compoundscontaining a cyclo-pentanoperhydro-phenanthrene nucleus. Moreparticularly it pertains to the preparation of such compounds fromM-Z-hydroxy-steroid esters. Still more particularly, it relates to theremoval of acid groups from A -7-hydroxy-steroid esters wherebyA,7-dehydro-steroid compounds are formed. In one of its preferredembodiments, it pertains to the preparation of 7-dehydro sterolmonocarboxylic acid esters and 7-dehydro sterols from A -7-hydroxy-sterol monocarboxylic acid esters. The invention also relates tonovel procedural conditions, assistants and processes for preparing such7-dehydrosteroid compounds.

The thermal decomposition of diesters of certain 7--hydroxy-steroids,namely, diesters of 7- hydroxy-sterols and monocarboxylic acids, atreduced pressures has been described in U, S. P. 2,098,984. Under theconditions specified therein small yields of 7-dehydro-sterol esters areformed. 'I-clehydro-sterol esters and 7-dehydro-sterols have also beenprepared from such diesters of steroids by treatment with organicnitrogenous bases such as organic amines until an acid group has beenremoved. See U. S. P. 2,209,934. The 7-dehydro esters are thensaponified to eld 7- dehydro sterols. The use of oxonium salt formingcompounds in the place of all or part 0 such bases with or withoutadditional assisting agents in addition has been described in U. S. P.2,255,815.

While these above described processes have some utility, they have somecommercial disadvantages and could be improved upon. The thermaldecomposition at elevated temperatures, for instance, requires verycareful supervision. Furthermore, the use of a high degree of vacuuminterposes economic and practical difliculties of operation. Inaddition, the heating of the ester melt causes decomposition o1 usefulproducts into those of no economic value.

The organic nitrogen bases and oxonium salt forming compounds haveutility but are somewhat expensive and are sometimes diflicult toobtain.

This invention has for an object the provision of new and practicalprocesses for producing '7- dehydro-steroid compounds. A further objectis the provision of processes of forming 7-dehydrosteroid compoundswhich eliminate uneconomic by-product formation. Another object is toprovide processes formaking 7-deliydro-steroid compounds which can becarried out in simple and economical apparatus. Another object is toproprocesses of removing acid groups from esterified M-l-hydroxy-steroidcompounds and to promote a general advance in this art.

The above objects are accomplished and the above disadvantages of priorart processes overcome by the invention hereinafter described.

It has been found according to one aspect of the invention, that7-dehydro-steroids can be obtained in increased yields by heating .A-7-hydroxy-steroid esters in a liquid hydrocarbon medium containingcertain assisting agents. The heating is continued until a materialamount of acid has been removed from the esters. The acid formed is thenseparated from the reaction mixture and the 7dehydro-'-steroid compoundsfurther processed.

In a more limited sense, it has been found that the decompositionreaction of selectively splitting out one mol of acid, especially anorganic monocarboxylic acid, from A -7-hydroxy-steroid esters byutilizing a liquid hydrocarbon medium, can be accelerated by a number ofassisting agents which possess the following characteristics: (a) theyare essentially insoluble in the solvent used, (b) they arenon-destructive of A -7-hydroxy-steroid esters and (0) they possess anactive surface.

In a further, more specific aspect of the invention it has been foundthat 7-dehydro-steroid compounds can be made by heating A-7-hydroxysteroid esters in a liquid medium containing at least oneassisting agent having the above-described general properties, but whichis further characterized in that it is insoluble in the liquid medium,solid and porous. Suitable materials of the last mentioned type include,solid water-insoluble metal powders, active or activated carbonsincluding activated charcoals and activecarbon, metal oxides,carborundum, powdered glass, silica gels, etc.

The last mentioned embodiment of the invention is not limited to the useof liquid hydrocarbon 'media. Various other solvents or diluents whichare non-destructive of 7-dehydro-steroid esters duce 7-dehydro-steroidcompounds in increased yields. Still other objects are to provide noveland steroids may be used in place of or in admixture with suchhydrocarbon media. The useful solvents may be acid binding agents orassist in the removal of acid groups from A -7-hydroxysteroid esters.Among these useful solvents are organic nitrogen bases such as aminesand oxonium salt forming compounds; suitable compounds of each of theseclasses are set forth in U S. patents, 2,209,934 and 2,255,815.

Referring now to the hydrocarbon media aspects of the invention, it hasbeen found that the splitting out of organic acid groups from esteriisobtained.

fied 7 -hydroxy-steroid compounds can be accelerated by the use ofinorganic salts which'have a pH range in water between 5 and 12 andmetal oxides in addition to the solid water-insoluble, pgrous,active-surface assisting agents described a ove.

In order to determine whether a compound meets with the requirements foran assisting agent as outlined above, the following simple tests shouldbe carried out.

(a) Test for insolubility The compound to be tested should be mixed withthe solvent-to be used and heated to about 100 C. If the compound to betested is essentially insoluble, it conforms with the insolubilityrequirement of the class of assisting agents.

(b) Tests for destructive properties Two milligrams of ergosterol or asimilar compound are heated in the presence of the compound to be testedand a hydrocarbon, for example, cyclohexane, in a. sealed tube to 200 C.for onehour. The reaction product is diluted with ethyl alcohol andspectroscopically examined for the presence of ergosterol bands. Thecompounds in question is suitable if the ergosterol is not destroyed.

(0) Test for active surface properties The compound to be tested asassisting agents should be added in small amounts to carbonated water.If the compound to be tested has surface active properties, carbondioxide gas evolves at a high speed, whereas when the compound to betested has no or only slight surface active properties, no or only asmall amount of carbon dioxide evolves.

The beneficial action of the assisting agents determined by the abovetest is quite surprising,

unexpected and diflicult to explain. It is possible that physical aswell as chemical phenomena are involved. The beneficial effect of theagents is illustrated in the following exemplary proce dures:

When 'l-hydroxy-cholesterol-dibenzoate is heated in cyclohexane at 183C. for 75 minutes followed by saponification of the reaction product, ayield of about 1% 'I-dehydro-chloesterol is obtained. 0n the other handwhen the same reaction is carried out in the presence of aluminum oxide,a yield of 10-12% 7-dehydrochloestrol is obtained. When the samereaction mixture is heated to 200 C. for 14 hours, about 46%7-dehydro-cholestrol is obtained without using assisting agents, whilein the presence of sodium chloride, 70-80% 'l-dehydro-cholesterol Theinvention will be further illustrated but is not intended to be limitedby the following examples;

Example I and the remaining cyclohexane solution subjected todistillation until only a small amount remains. The residue is cooledwhereby 7-dehydro-cholesterol crystallizes out. 32% of7-dehydro-cholesterol is obtained.

Example 11 7-hydroxy-cholesterol-dibenzoate is dissolved in cyclohexanein a molecular ratio of 1:40 and an equimolecular amount of sodiumchloride is added. The mixture is heated in a sealed system for 8 hoursat 200 C The reaction product is filtered from the sodium chloride aftercoolin and the benzoic acid formed during this reaction is extractedwith an aqueous sodium hydroxide solution. From the remainingcyclohexane solution, 7-dehydro-cholesterol-benzoate is obtained in ayield of 75-80% after the manner set forth in Example I.

The same reaction, using tetralin (tetrahydronaphthalene) instead ofcyclohexane, and refluxing the mixture for 2 hours, gave a yield of60-65.%

Example III 7-hydroxy-cholesterol-dibenzoate is dissolved in cyclohexaneand carborundum is added as an assisting agent. The reaction mixture isheated to 200 C. for 14 hoursin a closed system. The reaction product isthen worked up according to the procedure outlined in Example 1 wherebya yield of 82% of 7-dehydro-cholesterol-benzoate is obtained. Example IV7-hydroxy-cholesterol-dibenzoate is dissolved in cyclohexane and copperpowder is added. The mixture is heated to 200 C. in a sealed system. Thereaction product is worked up as described in Example I. A yield of50-60% of theory of 'ldehydro-cholesterol-benzoate is obtained.

Example V Three parts of 'l-hydroxy-cholesterol-diluenzoate and 3 partsof activated charcoal are mixed with 20 parts of cyclohexane and areheated in a sealed system to 150 C. for 2 hours. After cooling, thereaction product is filtered from the charcoal which in turn isextracted with ether. The combined extracts are washed with sodiumcarbonate solution to remove benzoic acid. After y n over sodium sulfatethe solution is concentrated and to the concentrate, acetone is added.'l-dehydro-cholesterol-benzoate crystallizes out. Yield=58.3%.

' Example VI spond to a yield of 69% of theory.

Example VII Three parts of 7-hydroxy-cholesterol-dibenzoate, '3 parts ofcarborundum and 25 g. of pyridine are heated in a sealed system to'190C. for 1.5 hours. After cooling, the mixture is filtered and thefiltrate poured on ice and water and ex- A yield of tracted with ether.The ether solution is washed consecutively with dilute hydrochloricacid, diluted alkali'and water until neutral. After drying over sodiumsulfate, the ether is distilled off and acetone added to the residue.7-dehydro-cholesterol-benzoate crystallizes out in a'yleld of 55% oftheory.

It should be understood that the invention is not limited to thetreatment of the specific '7-hydroxy-sterol esters described in theworking examples. On the contrary, it embraces the treatment of steroidsgenerally wherein a doubl bond exists in a position adjacent to theesterified hydroxy group in the 7-position, regardless of whetheradditional 'substituents are also present in other positions in themolecule. Any ester compounds having thecyclo-pentano-perhydrophenanthrene skeleton may be used wherein theester group is in the '7-position and a double bond in the 5,6-position.Such substances are sometimes termed steroid or sterid compounds andinclude those having the nucleus referred to with or without side chainsincluding said chains with other functional groups such as oxo, hydroxyland carboxyl groups and their derivatives. Thus, the term steroidsincludes not only sterols, but also bile acids, plant heart poisons,saponines and sex hormones. Among the suitable polyesters of theabove-described types are esters of p-7-hydroxycholesterol,7-hydroxy-sitosteryl diesters, 7-hydroxy stigmasterol diester,3,7-dihydroxy--cholenic acid esters, A5-andro-stentriol-3,7,l7-triesters, and the corresponding esters ofpregnane series. Still other suitable esters include the simple or mixedcarboxylic esters of 7-hydroxy sterol compounds obtainable from acidssuch as nitrobenzoic, m-dinitrobenzoic, chlorobenzoic, toluic,phenylacetic, cinnamic, formic, acetic, propionic, butyric, valeric,etc. acids and their acid anhydrides and acid halides, e.g. acylchlorides. Any of the diesters disclosed in U. S. patents, Nos. 2,-209,923 and 2,215,727, for instance, may be used as starting materialsin the present processes.

In place of the specific hydrocarbons set forth in the above examplesthere may be substituted a wide variety of hydrocarbons which are stableand do not polymerize or react with the components of the reaction mediaat reaction temperatures, having the above-described characteristics.The useful hydrocarbons are not limited to any one particular type, onthe contrary, simple and mixed aliphatic'including cyclo-aliphatic,alicyclic, aromatic and aliphatically substituted aromatic hydrocarbonscan be used. The hydrocarbons may be substituted by innocuous groupssuch as chlorine, fluorine, etc. Preferred hydrocarbons are stable,normally liquid and liquid at atmospheric pressure at temperatures inexcess of 150 C.

As examples of suitable additional stable hydrocarbons mention is madeof methylcyclohexane, ethylcyclohexane, benzene toluene, xylene,naphthalene, dihydronaphthalene, decahydronaphthalene; pinene; heptane,octane, etc., petroleum, ether, benzine, ligroin and similar mineral oilfractions, etc.; halogenated hydrocarbons, e. g. dichloroethane,tetrachloroethane, chlorobenzene, dichlorobenzenes, chlorotoluene,benzotrifluoride, etc.

The quantity of hydrocarbon may be varied over a fairly wide range, e.g. from 1 to 100 parts of hydrocarbon per part of steroid ester. Ingeneral, higher yields are obtained by the use of an excess ofhydrocarbon. A preferred range is 5 to 25 parts of hydrocarbon per partof steroid ester.

The temperature and time may also be varied over a fairly wide range. e.g. from C. and less to 300 C. and over. A temperature from C. to 260C.-represents a preferred range. The time may vary from about 2 hours to16 hours and over depending somewhat on the temperatures employed. Forexample, 2 hours heating at 220 C., 6 hours at 200 0., and 16 hours at180 C., givesubstantially the same yields. It is not necessary, however,to convert all the diester to the 7-dehyd o compound. The reaction maybe cut short when partially complete. It may be conducted somewhatcontinuously by drawing off and crystallizing formed 7-dehydro compoundsand replenishing the reaction mixture.

Among the additional metal salts useful in the process which in 10%water solution have a pH between 5 and 12 inclusive are sodium acetate,sodium phosphate, potassium chloride, potassium bromide, potassiumacetate, potassium phosphate, sodium arsenite, etc. One or more of suchsalts can be used in hydrocarbon media.

Various other solid water-insoluble assisting agents which have a largeamount of surface area may be substituted in like manner for thecarborundum, copper powder and charcoal of the examples. Suitablespecific agents include aluminum oxide, zinc oxide, silver oxide, copperoxide, silica dioxide,.magnesium oxide, blood charcoal, bone charcoal,aluminum powder, zinc powder, tin powder, etc.

The amount of assisting agent may vary over a wide range. In general, anequimolecular amount should be used. However, amounts from mol to 10mols may be used if desired.

The nove1 procedures hereof constitute an important advance in the art.They find especial usefulness in the production of provitamins D from A-7-hydroxy-sterol esters. The yields are definitely superior to those ofthe prior art.

The use of the novel assisting agents of this invention has a number ofadvantages, the most important of which is the fact that it enables oneto obtain increased yields of A -7 dehydrosteroid products. Anadditional advantage resides in the fact that the assistants are readilyavailable. A still further advantage resides in the fact that theassistants are less costly than the acid binding agents previouslyproposed. The hydrocarbon media has some advantages also in that theyare inexpensive, readily available, and enable clear colored products tobe prepared. The highly porous activated surface assisting agents enablethe reaction to be carried out at a materially lower temperature whichprevents decomposition and has many other economic advantages.

As many apparently widely different embodiments of this invention maybe, made without departing from the spirit and scope thereof, it is tobe understood that I do not limit myself to the specific embodimentsherein except as defined by the appended claims.

I claim:

1. The process which comprises admixing an esterified 7-hydroxy sterolwith a stable hydrocarbon having a boiling point between 150 C. and 250C. having suspended therein as an assisting agent finely divided siliconcarbide to a temperature between 100 C. and 300 C. for a period of atleast one hour, extracting the acid produced and recovering a 7-dehydrosterol compound.

2. A process for thermally decomposing a diester of 'l-hydrcxy-cholesterol which comprises -dis'solvingsaid diester in astable hydrocarbon solvent having a boiling point between 150 C.

- and 250 C. and heating thefisultlng solution,

while maintaining the temperature thereofunivdroxy-cholesterol-dibenzoate which comprises form by suspendingthereinfinelyr divided; inv soluble heat-transferring particles. 3. Aprocess for thermally decomposing 'I-hydroxy-cholesterol-di-benzoatewhich comprises 4 dissolving said compound in a stable hydrocar b'onsolvent having a boiling point between 150 C. and 250 C. and heating theresulting solution, while maintaining the temperature thereof uniform bysuspending therein finely divided, insoluble heat-transferringparticles.

4. A process for thermal decomposing '7-hy-

